Process as well as gas heater for heating a carrier gas stream

ABSTRACT

A gas heater (1) and gas heater method heat a carrier gas flow. The gas heater includes a gas inlet (2) a gas outlet (3) and a connecting gas channel (4). A heating system (5), arranged in the gas channel, includes a heat exchanger (12) surface. The carrier gas at least partly flows over the surface to heat the carrier gas flow. The gas channel includes a first section (6), arranged upstream of the heat exchanger in a flow direction, and a second section (7) arranged downstream of the heat exchanger. A respective sensor (8a, 8b), for detecting a pressure value, is in the first and the second section or directly adjacent thereto. Pressure values are transmitted to a control and analysis unit (9) which ascertains a mass and/or volume flow of the carrier gas in the gas channel based on a pressure difference between the two pressure values.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a United States National Phase Application ofInternational Application PCT/EP2017/000876, filed Jul. 19, 2017, andclaims the benefit of priority under 35 U.S.C. § 119 of GermanApplication 10 2016 008 952.0, filed Jul. 26, 2016, the entire contentsof which are incorporated herein by reference.

TECHNICAL FIELD

The present invention pertains to a process as well as to a carrier gasheater, for heating a carrier gas stream, with a gas inlet and with agas outlet which are connected by a gas duct. A heater, which releasesheat to the carrier gas stream at least at times, is arranged in the gasduct between the gas inlet and the gas outlet in the flow direction ofthe carrier gas stream. The present invention further pertains to theuse of a corresponding gas heater in a device for heating a carrier gasstream which is fed to a patient at least at times during anesthesia inorder to supply the patient with an anesthetic as needed.

TECHNICAL BACKGROUND

A large number of anesthesia devices, with which an anesthetic is fed toa breathing gas stream for a patient for the temporary anesthetizationof the patient ventilated by the anesthesia device during this period oftime, are known from the state of the art. In this case, the temperaturecontrol of the carrier gas stream as well as the enrichment of thebreathing gas stream with volatile anesthetic are of considerableimportance, and the dispensing of an anesthetic as needed into thecarrier gas stream especially depends on the accurate temperaturecontrol of the carrier gas stream, and especially on maintaining thenecessary temperature. An excessively intensive cooling of the carriergas stream is, above all, problematic since there is then a risk thatnot enough anesthetic evaporates. Anesthetic evaporators that operatemechanically for dispensing an anesthetic into a carrier gas stream andthat are heated in a suitable manner by means of an electric heater havebeen known for many years.

The problem with mechanically adjustable anesthetic dispensers is thatthese require relatively large thermal storage masses, so that thedevice is prevented from cooling off when large evaporation mass flowsare required, and then an inadmissible lowering of the vapor pressureand thus of the vapor output to be dispensed would occur. Mechanicallyoperating anesthetic dispensers are often relatively heavy because ofthe required thermal storage masses, which in turn is disadvantageousfor handling.

Based on the problems mentioned above, efforts have been made to replacemechanically adjustable anesthetic dispensers, which are relativelyheavy especially because of the thermal storage masses, withelectronically controlled anesthetic dispensers. In this connection, thetemperature control of the carrier gas stream, to which the neededanesthetic shall be added, is of special importance.

In this connection, a device for dispensing an anesthetic into a carriergas stream is known from DE 10 2014 008 625 A1, in which a novelevaporation principle is used. The technical solution being described ischaracterized in that the heat needed for the evaporation of theanesthetic located in the anesthetic evaporator is introduced into theevaporation chamber of the anesthetic dispenser with the carrier gasstream as needed. The introduction of the necessary heat into thecarrier gas stream to be enriched with anesthetic takes place in thiscase as a function of the breathing gas volume flow needed for supplyingthe patient to be anesthetized as well as the anesthetic concentrationin the gas stream. The heat output is set as a function of an anestheticconcentration/volume flow measured in the breathing system as well ascorresponding set values predefined by the user.

SUMMARY

As the above explanations show, both the measurement of the breathinggas volume flow and the temperature of the carrier gas and the heatingthereof are of special importance for the exact feeding of an anestheticto a patient. Based on this problem, the basic object of the presentinvention is to provide a cost-effective, reliable and energy-efficientcombination of a volume flow measurement with a carrier gas heating. Atechnical solution to be specified correspondingly shall be integratedhere in a relatively simple manner in prior-art systems for theenrichment of a carrier gas stream with an anesthetic. Another,essential aspect of the present invention is that uncontrolled changesof the flow properties because of condensation, especially in the areaof measurement points, are avoided in a reliable manner, wherein theheat needed for this or the heat output of a heating element shall atthe same time be minimized.

The present invention pertains to a gas heater for heating a carrier gasstream with a gas inlet and with a gas outlet, which are connected by agas duct. Carrier gas stream in the sense of the present invention isdefined as a fluid stream, which contains air and/or at least one gas.Such a gas heater is thus capable of heating a gas, a mixture of atleast two gases, a mixture of air and at least one gas or air. A heaterwith at least one heat exchanger, which heater releases heat to thecarrier gas stream at least at times, is arranged in the gas ductbetween the gas inlet and the gas outlet in the flow direction of thecarrier gas stream. The present invention is characterized in that thegas duct has at least one first section, which is arranged in the flowdirection in front of the heat exchanger, as well as a second section,which is arranged in the flow direction behind the heat exchanger, thata sensor each is provided for detecting a pressure value in the firstsection and in the second section or directly adjacent hereto, and thatthe pressure values are sent to a control and analysis unit, whichdetermines a mass flow and/or a volume flow of the carrier gas stream inthe gas duct based on a pressure difference of the two pressure values.

The present invention is thus essentially characterized in that theheating of a carrier gas stream is combined with the detection of a massflow and/or volume flow of the carrier gas stream, i.e., a so-calledflow measurement, in one structural unit. The heating of a carrier gasstream as well as the measurement of a mass flow and/or volume flow canbe carried out in this manner in an especially efficient andspace-saving manner. The mass flow and/or volume flow is measured hereaccording to the principle of pressure difference, which is currentlyusually also used in the area of anesthetic dispensing. The gas heaterconfigured according to the present invention, which combines a heaterwith a device for measuring the mass flow and/or volume flow, can beused both for electronically controlled anesthetic dispensers and formechanically adjustable evaporators, in which a volatile anesthetic isevaporated as needed and is absorbed by a carrier gas stream. After theset-up of a gas heater, measurements are preferably carried out, withwhich especially the flow resistance of the heater arranged between thepressure sensors in the gas duct is determined in case of different flowproperties, i.e., in case of different volume flows and/or gascompositions. The recorded values are stored in the control and analysisunit of the gas heater or in a memory, which is set up to exchange datawith the control and analysis unit unidirectionally or bidirectionally,and the values are used as a basis for the determination of the massflow and/or volume flow carried out, taking into consideration thepressure difference prevailing between the two pressure sensors duringthe operation of the gas heater. The structural elements of the heater,especially the heat exchanger, arranged in the gas duct between thepressure sensors, quasi additionally assume the function of a measuringorifice for the determination of the mass flow or volume flow flowingthrough the gas heater during the operation of the gas heater. Thisillustrates the especially space-saving combination of a heater with ameasuring element for the detection of a volume flow or mass flow in agas heater.

The heater has a heating element which is supplied with energy from theoutside and which is thermally coupled to the heat exchanger in aspecial embodiment of the present invention. The carrier gas streamflows at least partly over the heat exchanger surface of the heatexchanger in the operating state. The heating element is preferably aheating element supplied with electric energy, for example, a heatingrod. It is also conceivable that the heating element is supplied withother heat-carrying media, for example, air, gas and/or vapor and theheat released by the heating element is finally released via the heatexchanger and here especially via the heat exchanger surface to thecarrier gas stream. It is also conceivable that the heating element is acomponent, which releases heat through heat conduction or heat diffusionor conduction to the heat exchanger. Such a heat conduction is broughtabout by a temperature difference, and the heating element is suppliedwith heat from a heat source, which is arranged outside of the gasheater and this heat is sent to the heat exchanger based on theprevailing temperature gradient and from this heat exchanger to thecarrier gas stream flowing through the gas heater.

Finally, the heating element may also be a radiation source, which heatsthe heat exchanger of the gas heater by heat radiation, especially IRradiation. Provisions are made according to a special embodiment of thepresent invention for the heating element and the heat exchanger,especially the heat exchanger surface, to be components of a structuralelement or to be integrated into a structural element.

It is always essential for the present invention that a heating elementbe provided, which releases its heat to a heat exchanger, which has arelatively large surface, so that the heat can be released over a largeheat exchanger surface to the carrier gas stream. Provisions are madeaccording to a special embodiment of the present invention for the heatexchanger to have ducts, ribs, open-pore structures or similargeometries, so that the transfer of heat to the carrier gas stream iscarried out along a surface that is as large as possible.

According to a special variant, the heat exchanger is made of anopen-pore, preferably sintered material. In this connection, a preferredvariant is for the heat exchanger to be made of an open-pore, sinteredmetallic material or ceramic material. Such a metallic material orceramic material may especially be a metallic foam or ceramic foam, forexample, an aluminum foam.

The heat exchanger preferably has at least one recess, in which theheating element is arranged. It is conceivable in this case that theheat exchanger has a disk-like or cylindrical configuration in at leastsome parts and the heating element is arranged in a recess that islocated in a disk or a cylinder of the heating element. A so-calledsintered diaphragm or a sintered cylinder made of sintered material,especially made of sintered ceramic or sintered metal, is especiallypreferably used, in the interior of which is arranged a heating element,for example, in the form of a cylindrical cartridge-type heater, whichis supplied with electrical energy for heating.

According to a special embodiment, a layer reflecting heat radiation isprovided, which is arranged between the heat exchanger and a jacketelement enclosing the heat exchanger in at least some areas. The heatingelement is thus preferably at least partially jacketed by the jacketelement. In this case, it is, in principle, irrelevant whether such ajacket element is the outer housing of the gas heater itself or else acomponent wall enclosing the heat exchanger, which component wall islocated in the interior of the gas heater. It is always essential forthe layer reflecting heat radiation that the heat radiation originatingfrom the heat exchanger be reflected effectively, so that, on the onehand, an energy-efficient heating of the carrier gas stream in the gasduct is guaranteed and, on the other hand, an inadmissible heating ofthe outer housing of the gas heater is avoided.

According to a very special embodiment, the jacket element is configuredin the form of a tube, i.e., a jacket tube, in which the heat exchangerwith the heating element located in it is arranged. The layer reflectingheat radiation, which reflects heat radiation originating from the heatexchanger in the direction of the heat exchanger, is preferablyconfigured in the form of a film, which is applied to the outer surfaceof the heat exchanger and/or to a surface of the jacket element facingthis heat exchanger. According to another alternative embodiment, thelayer reflecting heat is configured in the form of a coating, which isapplied to a surface of the jacket element facing the heat exchanger.

In a special embodiment of the present invention, at least onetemperature sensor is arranged in the gas duct. The at least onetemperature sensor is preferably arranged in the heat exchanger. Thetemperature values detected by the at least one temperature sensor aresent to a control and analysis unit, which can preferably actuate theheating element, taking the detected temperature values intoconsideration, and thus can influence the introduction of heat into theheat exchanger and finally into the carrier gas stream. Such a controland analysis unit is advantageously either connected to the centralcontrol unit of a device for dispensing anesthetic into the carrier gasstream or is part of such a control unit or is integrated into thiscontrol unit. It is ensured in this way that the heating element can beactuated in a targeted manner and the temperature of the carrier gasstream can be set at a needed value, taking into consideration thetemperature detected in the gas duct of the gas heater and/or othermeasured values, which are recorded in the device for dispensing ananesthetic into a carrier gas stream, and/or set values, which arepredefined by the user. Thus, for example, cooling effects, which arebrought about because of the evaporation of an anesthetic in ananesthetic evaporator, can be offset precisely and rapidly in anespecially reliable manner.

Furthermore, it is also conceivable to use the temperature values, whichare detected by at least one temperature sensor and which are sent to acontrol and analysis unit, to determine a characteristic temperature,especially a temperature characteristic for the area of the transfer ofheat from the heat exchanger to the carrier gas stream, whichcharacteristic temperature is included in an algorithm for thetemperature compensation of the pressure difference-volume flowmeasurement, on the basis of these detected temperature values. Theoften relevant temperature drifts of the materials, media and/oroperating materials used, i.e., the temperature-dependent change in thephysical properties of these materials, can be taken into considerationin this manner.

According to a very special variant of the present invention, at leasttwo temperature sensors, which are each spaced apart from one another inthe gas duct and which send the measured temperature values to a controland analysis unit, are provided, and a control signal is generated inthe control and analysis unit for the operation of the heater based on atemperature difference between the at least two temperature valuesdetected by different temperature sensors or taking into consideration atemperature gradient and/or a characteristic temperature value for thetemperature compensation of the pressure difference-volume flowmeasurement.

At least one of the two pressure sensors provided in the gas heater isadvantageously arranged in a flow-calmed area. Flow-calmed area in thesense of the present invention is considered to be an area in the gasduct or in the adjoining flow space, in which the gas located thereflows relatively slowly or the flow even stops at least at timescompared to the rest of the gas duct, and especially compared to theinterior of the heat exchanger.

Moreover, the present invention pertains to a device for heating acarrier gas stream, which is fed to a patient at least at times duringanesthesia, which has a gas heater, as it has been described above. Sucha device is especially characterized in that the gas heater is arrangedin the flow direction of the carrier gas stream in front of or behind ananesthetic dispenser, which adds an anesthetic to the carrier gas streamat least at times. The anesthetic dispenser is preferably an anestheticevaporator, which adds a volatile anesthetic to the carrier gas streamby way of the evaporation principle, and the gas heater is fluidicallyconnected in series with the anesthetic dispenser. The device configuredaccording to the present invention thus contains a cost-effective,reliable and energy-efficient combination of flow measurement andcarrier gas heating, which is especially advantageous for the anestheticdispensing by means of electronically controlled dispensers. Here aswell, the volume flow is measured on the basis of a pressure differencemeasurement, wherein it is reliably ensured by the technical solutionaccording to the present invention that condensation is avoided in thearea of the measured path. An essential advantage of the use of a gasheater configured according to the present invention in conjunction withan anesthetic dispenser is that the heat output needed for the as-neededheating of the carrier gas stream to be enriched with anesthetic isrelatively low compared to prior-art heaters.

The present invention pertains, moreover, to a process for heating acarrier gas stream, in which a carrier gas stream is fed to a gas ductvia a gas inlet and from which the carrier gas stream is released via agas outlet. The carrier gas stream is heated at least at times by aheater arranged between the gas inlet and the gas outlet. The processconfigured according to the present invention is characterized in that apressure value each is detected in the gas duct in a first section,which has a first flow cross section, as well as in a second section,which has a second flow cross section that is different from the firstcross section, the pressure values are sent to a control and analysisunit, and a volume flow of the carrier gas in the gas duct is determinedin the control and analysis unit based on a pressure difference of thetwo pressure values. According to a special variant of the processaccording to the present invention, at least one temperature is measuredin the gas duct and/or in a component located in the gas duct oradjoining the gas duct. A control signal, on which are based theoperation of the heater and/or a calculation of the volume flowprevailing in the gas duct on the basis of the detected pressure values,is preferably generated based on this detected temperature.

Provisions are made in a special variant of the present invention forthe pressure measurements to be carried out in an area of the gas duct,in which the flow is calmed. For example, the pressure measurement iscarried out in an area in front of or and/or behind the heat exchanger,which is thermally coupled to the heating element and through which thecarrier gas stream flows. While a turbulent flow preferably prevailswithin the heat exchanger, a laminar flow prevails in the area, in whichthe pressure measurements are carried out, or the flow even stops attimes.

The present invention will be explained in more detail below withoutlimiting the general idea of the present invention on the basis ofexemplary embodiments or reference to the figures. The various featuresof novelty which characterize the invention are pointed out withparticularity in the claims annexed to and forming a part of thisdisclosure. For a better understanding of the invention, its operatingadvantages and specific objects attained by its uses, reference is madeto the accompanying drawings and descriptive matter in which preferredembodiments of the invention are illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a schematic cross-sectional view of a gas heater withintegrated pressure measurement points;

FIG. 2 is a schematic cross-sectional view of a gas heater withintegrated pressure measurement points and temperature sensors;

FIG. 3 is a coaxially configured sintered gas heater with integratedpressure difference measurement and self-cooling housing;

FIG. 4 is a graphic diagram of the pressure loss curve in case ofvariable volume flow;

FIG. 5 is a graphic diagram of the heating of the carrier gas stream asa function of the heating time; and

FIG. 6 is a schematic sectional view of a gas heater.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to the drawings, FIG. 1 shows a schematic cross-sectional viewof a carrier gas heater 1 which is configured according to the presentinvention, and which has a carrier gas heater body with a gas inlet 2and a gas outlet 3, which are connected to one another via a gas duct 4defined by the carrier gas heater body. A rod-shaped heating element 11,which can be supplied with electric energy, and on which are arranged aplurality of disk-shaped sintered elements, forming a heat exchanger 12,is provided within the gas duct 4. The disk-shaped sintered elementshave in their center a hole 13, so that the sintered disks can be pushedover the heating element 11 and can be in thermal contact with same. Ifthe heating element 11 is supplied with electric energy, then thisheating element is heated, and the heat is transferred to the sintereddisks being used as heat exchanger 12.

The disks used in this exemplary embodiment are made of a sinteredceramic that has an open-pore structure, so that the surfaces of thedisks are each connected to one another by small flow ducts. Theopen-pore structure is essential here, above all, so that othermaterials may also be used instead of a sintered ceramic. In this way, aheat exchanger 12 is provided, which has an especially large surface,along which the heat is transferred to the carrier gas stream.

The heating element 11 with the heat exchanger 12 fastened to it, whichheat exchanger has a plurality of sintered disks, is enclosed by ajacket element 10. In the exemplary embodiment being shown in FIG. 1,the jacket element 10 is configured in the form of a jacket tube, intowhich the heating element 11 has been inserted together with the heatexchanger 12. A layer 15 reflecting infrared radiation is applied on theinside of the jacket element 10, which is configured as a tube, in orderto be able to reflect the heat radiation originating from the heatingelement 11 as well as from the heat exchanger 12 into the gas duct 4 atleast to a great extent. The layer 15 reflecting infrared radiation isin this case configured in the form of a film, which is applied to theinside of the jacket element 10 being used as jacket tube. It is alsoconceivable that a coating 15 reflecting infrared radiation is appliedto the inner surface of the tube 10 in addition to or as an alternativeto a film.

The gas heater 1 being shown in FIG. 1 has in its interior two sections6, 7, which are arranged in the area of the gas duct 4 and between whichis located a fluidic narrow space or constricted space, in the area ofwhich a part of a heating element (11) as well as the heat exchanger(12) of the heater 5 are arranged. In the first section 6, which isarranged in the flow direction in front of the heat exchanger 12, and inthe second section 7, which is arranged in the flow direction behind theheat exchanger 12, are arranged pressure measurement points 8 a, 8 b,respectively, at which the pressure prevailing in this area is detectedand is sent to a control and analysis unit 9. A pressure difference isdetermined from the respective pressure value detected at a time and thevolume flow of the carrier gas flowing through the gas duct 4 iscalculated, taking the determined pressure difference intoconsideration. The increase in the flow rate at the constricted spacebrings about a reduction of the static pressure corresponding toBernoulli's energy equation, so that there is a pressure differencebetween the two pressure measurement points 8 a, 8 b, which pressuredifference is also called differential pressure and represents anindicator of the flow, i.e., the volume flow and/or mass flow, underknown hydraulic conditions. The constricted space between the firstsection and the second section 7 of the gas duct 4 with the heatexchanger 12 of the heater 5 provided therein thus represents a type ofmeasuring orifice, the flow resistance of which is used for determiningthe volume flow and/or mass flow. After the set-up of the gas heater, ithas to carry out measurements only once in relation to its hydraulicproperties, especially the flow resistance of the heat exchanger 12, andrecorded values are stored in the control and analysis unit 9 or in amemory connected to same, so that these values can be taken intoconsideration in the determination of the volume flow or mass flowflowing through the gas heater 1 during the operation on the basis ofthe measured pressure difference.

As an alternative, it is conceivable that other pressure sensors 8, forexample, a Pitot tube or Prandtl probe, are also used for determiningthe pressure difference between the two pressure measurement points 8 a,8 b. These sensors take into consideration the energy conservation lawin the form set up by Bernoulli. In this case, it is taken intoconsideration that the kinetic energy of the carrier gas stream can beconverted. If a change in the flow cross section occurs, this means thatthe flow rate of the flowing fluid and thus also the pressure change.The pressure prevailing in the fluid as well as the flow rate are thusdirectly related.

The gas heater 1 being shown in FIG. 1 has, furthermore, a housing 14,in which are arranged the gas duct 4 with the pressure measurementpoints 8 a, 8 b as well as the heating element 11 with the heatexchanger 12, which represent the principal components of the heater 5of the gas heater 1. An insulation or thermal insulation 16, whichcounteracts an inadmissible heating of the housing 14, is provided inthe area between the housing 14 and the heat exchanger 12 with theheating element 11 arranged in it. Since a small gap 19, in which apartial stream of the carrier gas flows from the gas inlet 2 to the gasoutlet 3, without flowing through the heat exchanger 12, preferablyremains between the heat exchanger 12 and the jacket tube 10 enclosingsame, a further cooling between the heat exchanger 12 and the housing 14is achieved. An inadmissible heating of the jacket tube 10 is reliablycounteracted by this feature. The radial temperature gradient developingwithin the carrier gas stream in this connection, namely the temperaturedifference between the carrier gas stream in the interior of the heatexchanger 12 and the carrier gas stream in the area of the gap 19between the heat exchanger 12 and the jacket tube 10 is knowinglyaccepted.

According to FIG. 1, a slim, electric cartridge-type heater as heatingelement 11 is thus inserted into a heat exchanger 12, which ismanufactured from a plurality of cylindrical diaphragms that are made ofa sintered ceramic material, and the gas heater 1 thus formed iscombined with a volume flow measurement.

The heat output of the electric cartridge-type heater 11 used is in arange of up to 30 W. The pressure measurement connections 8 a, b areeach located in a flow-calmed area 18, 20 in front of and behind theheat exchanger 12, respectively, so that a reliable pressure measurementis made possible. Inadmissible heating is prevented by the carrier gasto be heated flowing by in the direct vicinity of the jacket tube 10 onthe inside of same in the gap 19 provided for this. It is, moreover,possible due to the integrated flow measurement to operate the heater 5in proportion to the respective determined flow.

Further, a characteristic temperature, which is included in an algorithmfor the temperature compensation of the pressure difference-volume flowmeasurement, is determined in the sintered ceramic heat exchanger 12 bymeans of suitable temperature sensors 17 a, 17 b. In this manner, therelevant temperature drifts of the substance data of the materials beingused in the gas heater 1 are offset. As can be seen in FIG. 1, twotemperature sensors 17 a, 17 b, which are arranged spaced apart from oneanother within the heat exchanger 12, are provided according to thisexemplary embodiment. According to the exemplary embodiment shown inFIG. 1, the two temperature sensors 17 a, 17 b are each arranged behindone another in the flow direction in different disks of the heatexchanger 12.

Complementary to FIG. 1, FIG. 2 likewise shows a cross-sectional view ofa gas heater 1, in which a volume flow measurement is carried out bymeans of two pressure sensors 8 a, 8 b. In this case as well, the gasduct 4, which extends from a gas inlet 2 up to a gas outlet 3 of the gasheater 1, has two sections 6, 7, between which is located a narrow spaceor constricted space with a heat exchanger 12 arranged in this area. Ineach of these areas 6, 7 is located a pressure measurement point each,in which the static pressure prevailing in the flowing carrier gas isdetected by means of a pressure sensor 8 a, 8 b and is sent to a centralcontrol unit 9.

A heat exchanger 12, which has a disk-shaped or cylindricalconfiguration, is in turn arranged in the interior of the gas duct 4.This heat exchanger 12 is heated by means of an electrical heatingelement 11, which is fastened to the heat exchanger 12 within same, sothat a carrier gas flowing through the gas heater 1 absorbs heat fromthis heat exchanger during the flow through the heat exchanger 12.Within the gas duct are provided three points, at which the temperatureprevailing in this area is detected by means of temperature sensors 17a, 17 b, 17 c, respectively. The three temperatures are likewise sent toa control and analysis unit 9. A characteristic temperature for the heatexchanger 12, on which are based the actuation of the heating element 11and/or the calculation of a volume flow value, is calculated by means ofthe control and analysis unit 9 on the basis of the determined threetemperatures. It is of special importance here that the substance data,which are respectively relevant for the heat conduction, especially theheat-conducting components, can be taken into consideration in thedetermination of the volume flow based on the determined temperatures orthe temperature gradient prevailing in the area of the heat exchanger12.

FIG. 3 likewise shows a sectional view of a gas heater 1 configuredaccording to the present invention, in which a volume flow determinationof the carrier gas stream flowing through the gas heater 1 is carriedout. Especially the individual components of the gas heater 1 can beseen here in FIG. 3. The heat exchanger 12, which has an open-porestructure, is configured in the form of a cylinder. A hole, into whichis inserted a heating element 11, which is supplied with electricenergy, is provided as a recess 13 in the interior of the cylinder. Theheat exchanger 12 with the heating element 11 arranged in it is enclosedby a jacket element 10, which is configured as a tube.

The flow path of the gas heater 1 is formed by a gas inlet 2 and a gasoutlet 3 as well as a gas duct 4 connecting the gas inlet and the gasoutlet 2, 3. After the carrier gas stream flows into the gas heater 1through the gas inlet 2, the carrier gas flows through the heatexchanger 12, is heated here and finally flows out of the gas heater 1again through the gas outlet 3.

On its side facing the gas inlet 2, the jacket tube 10 is attached to aconnection surface of a sealing disk 21, the jacket tube 10 is beingpositioned and clamped between this disk 21 and a conical spring 22. Awasher 24, which assumes essentially two functions, is provided betweenthe conical spring 22 and the jacket tube 10. On the one hand, theconical spring 22 is centered in relation to the jacket element 10 bymeans of the washer 24 and the contact pressure originating from thespring 22 is evenly transferred to the jacket tube 10 and, on the otherhand, the heat exchanger 12, here in the form of filaments, is fixed inits position.

The sealing disk 21, which has a circular-ring-shaped inlet opening 23for the flowing carrier gas stream, is inserted or pressed into thehousing 14 with a slight interference fit on its circumferentialsurface. It is ensured in this manner that the carrier gas stream intothe gas heater 1 fully reaches the jacket tube 10, in which the heatexchanger 12 with the heating element 11 is located.

The sealing of the housing 14 of the gas heater is brought about bymeans of a housing cover 25, which has a two-part configuration and issealed via O-rings against the housing 14 as well as against the heatingelement 11, which passes through the housing cover 25.

In order to limit heat losses, a polyimide film 15, which prevents acontact between the hot carrier gas and the jacket tube 10 andfurthermore with the housing 14, is provided on the inner side of thejacket tube 10. This film 15 reflects infrared radiation at least to agreat extent, so that the infrared radiation coming out of the directionof the heating element 11 as well as of the heat exchanger 12 is againreflected back in the direction of the heat exchanger 12. The polyimidefilm 15 jackets the heat exchanger 12 and is clamped on the side facingthe gas inlet 2 between the sealing disk 21 and the jacket tube 10. Thepolyimide film is arranged on the side facing the gas outlet 3 and isconfigured in the form of a funnel, which passes over into a hollowcylinder, such that the carrier gas flowing out of the heat exchanger 12and the jacket tube 10 within the film 15 leaves the gas heater 1 viathe gas outlet 3.

Further, an insulating material 16, especially an insulating fibrousmaterial, which contains ceramic wool in this case, is provided betweenthe jacket tube 10 and the housing 14 of the gas heater 1. Thisinsulation counteracts a heat conduction from the jacket tube 10 ontothe housing 14 at least to a considerable extent.

Pressure sensors 8 a, 8 b, which detect the pressure in the carrier gasin comparatively flow-calmed areas 18, 20 and send same to a control andanalysis unit 9, are each arranged in these areas 18, 20 both in thefirst section 6 in front of the heat exchanger 12 and in the secondsection 7 behind the heat exchanger 12. A pressure difference isdetermined in the control and analysis unit 9 on the basis of thedetected pressure values and from this a volume flow of the carrier gasflowing through the gas heater 1 is determined according to the rules ofthe pressure difference method. Because of the heating of the gas duct4, the carrier gas can, on the one hand, be heated to a temperatureneeded for the use of the carrier gas for a further process, forexample, for the enrichment with anesthetic, and, on the other hand, itis ensured that condensation effects, which would interfere with thedetermination of the volume flow in the interior of the gas heater 1,are largely ruled out.

Furthermore, temperature sensors 17 a, 17 b, which detect the respectivetemperature in this area and likewise send same to the control andanalysis unit 9, are provided at different points of the heat exchanger12. A temperature difference or temperature gradient is determined fromthe determined temperatures, so that a characteristic temperature canfinally be determined for the heat exchanger 12, which is included in analgorithm for the temperature compensation of the pressuredifference-volume flow measurement. The relevant temperature drifts ofthe substance data of the components involved in heat conduction areherewith taken into consideration and can be offset by means of suitableactuation of the heating element 11.

Condensation in the area of the gas heater 1, especially at the pressuresensors 8 a, is avoided with certainty by means of the technicalsolution described. Furthermore, the heat output necessary for theheating is limited to an economically significant extent. Acharacteristic gas temperature for calculating the volume flow and formonitoring the heating element 11 can be determined and the carrier gasstream can be heated in an energy-efficient and reliable manner with amoderate drop in pressure and with relative low excess temperatures. Thedrop in pressure between the two pressure sensors 8 a, 8 b is about 30mbar at a volume flow of 5 L/min during the normal operation.

FIG. 4 shows for this the measured values recorded with a prototype of agas heater 1. The volume flow of a carrier gas stream, here an airstream, flowing through the gas heater 1 is plotted on the X axis in arange of 0 L/min to 8 L/min, while the pressure difference between thetwo pressure sensors 8 a, 8 b is plotted on the Y axis in a range of 0mbar to 60 mbar.

A gas heater 1 configured according to the present invention canpreferably be used in connection with anesthetic dispensers, as they areused in modern anesthesia apparatuses. A carrier gas stream, which isfed to the anesthetic dispenser, especially to an anesthetic evaporator,can be heated by means of such a gas heater 1 to the requiredtemperature and at the same time the mass flow and/or volume flow of thecarrier gas stream flowing through the gas heater can be determined. Thegas heater is preferably arranged in the flow direction of the carriergas in front of the anesthetic evaporator. In principle, however, it isalso conceivable to arrange a correspondingly configured gas heater inthe flow direction downstream of the anesthetic dispenser as a functionof carrying out the anesthetic dispensing.

Since not only the temperature of the carrier gas stream, but also thevolume flow thereof is of decisive importance for the enrichment of acarrier gas stream with a quantity of anesthetic needed for theanesthetization of the patient, a gas heater 1 configured according tothe present invention represents a component which can be used in anespecially advantageous manner, because both a heating of the carriergas and the determination of the volume flow can be achieved in a highlyprecise and yet energy-efficient manner. Compared to conventionalanesthetic dispensers, which often have external heat sources andrelatively large thermal masses to prevent an inadmissible cooling ofthe anesthetic dispenser, the above-described gas heater, which isintegrated into the gas circuit, requires a relatively low heat outputin order to heat up the carrier gas stream to the needed temperature andto reliably counteract a cooling of the anesthetic evaporator, whichcooling occurs in case of removal of a large quantity of vapor.

In this connection, FIG. 5 shows a graphic diagram of values, as theywere again recorded with the prototype of a gas heater. In this case, acarrier gas stream with a volume flow of 8 L/min flowed through the gasheater used. The maximum heat output of the heating element used was 30W. After 28 sec, the output was reduced and was only 17.2 W to 17.7 Wfor the remaining time of the test shown in FIG. 5.

A time period of 0 min to 7 min is plotted on the X axis in the diagramshown in FIG. 5. The values plotted on the Y axis correspond totemperatures in a range of 0° C. to 160° C. The function curve T₂ showsthe temperature of the housing of the gas heater 1 over the plotted timeperiod of 0 min to 7 min. As can be seen, the temperature T₂ of thehousing increases only by about 17 K, namely from 22° C. to 39° C.because of the film reflecting infrared radiation provided in theinterior, because of the cooling gap and because of the thermalinsulation additionally provided between the jacket element and thehousing. Contact with the housing is thus possible without problems,especially without this being connected with risks for the user.

The function curve T₁ represents the temperature of the carrier gasstream at the gas outlet 3, and air was used as the carrier gas in thetest in question here. The temperature value increases to 120° C. atfirst within about 28 sec and remains approximately constant at a valueof 105° C. over the next 6.5 min. In this case as well, the decrease inthe temperature after 5 min can be attributed to a change in the volumeflow from 0.00775 m³/min to 0.008 m³/min.

It is essential, above all, at the temperature curves T₁, T₂ shown inFIG. 5 that a carrier gas temperature T₁ be already reached at the gasoutlet 3 after about 30 sec despite relatively low heat output, whichtemperature continues to remain almost constant.

A cylindrical cartridge-type heater was used as the heating element (T+H0214 HLP (d5; L60; 100 W; 24 V), which is thermally coupled to the heatexchanger, which consisted on five disks made of porous aluminum with apore diameter of 200 m to 250 m.

Further, FIG. 6 shows a schematic sectional view of a gas heater 1configured according to the present invention, wherein the sectionalplane is arranged at right angles to the main direction of extension ofthe gas heater and thus to the main direction of flow of the carriergas. An essential feature of the embodiment being shown is that the gasinlet 2 and especially the inflow direction is arranged in parallel andat a vertical distance to the center line running from top to bottom inthe drawing plane. It is ensured in this manner that the carrier gasflowing in can flow evenly along the circumference in the inflowsection. Finally, a flow develops, which is directed in a funnel-shapedmanner towards the inlet of the heat exchanger or towards the inletopening shown in FIG. 3 in the sealing disk 21. The pressure measurementpoint for the first pressure sensor 8 a, viewed in the flow direction,can be seen on the side of the center line located opposite the gasinlet.

It is essential for the described solution according to the presentinvention that a gas heater be provided, with which a volume flow of thecarrier gas can be determined simultaneously with the heating of acarrier gas stream, wherein both the heating and the determination ofthe volume flow are achieved in a highly precise and energy-efficientmanner.

While specific embodiments of the invention have been shown anddescribed in detail to illustrate the application of the principles ofthe invention, it will be understood that the invention may be embodiedotherwise without departing from such principles.

The invention claimed is:
 1. A carrier gas heater for heating a carriergas stream, the gas heater comprising: a gas duct with a gas inlet andwith a gas outlet, which are connected by the gas duct; a heaterarranged in the gas duct at least partly between the gas inlet and thegas outlet in a flow direction of the carrier gas stream, the heatercomprising a heat exchanger with a heat exchanger surface which thecarrier gas stream flows over at least partly in an operating state, sothat the heat exchanger at least at times releases heat to the carriergas stream, wherein the gas duct comprises at least one first sectionarranged in the flow direction in front of the heat exchanger and asecond section arranged in the flow direction behind the heat exchanger,wherein the heater further comprises a heating element and the heatexchanger is thermally coupled to the heating element, which is suppliedwith energy from outside of the carrier gas heater; a first sensorprovided for detecting a pressure value in the first section or directlyadjacent hereto; a second sensor provided for detecting a pressure valuein the second section or directly adjacent hereto; and a control andanalysis unit wherein the detected pressure values are sent to thecontrol and analysis unit and the control and analysis unit isconfigured to determine a mass flow and/or volume flow of the carriergas stream in the gas duct based on a pressure difference of thedetected pressure values.
 2. A carrier gas heater in accordance withclaim 1, wherein the heat exchanger and the heating element form astructural unit.
 3. A carrier gas heater in accordance with claim 1,wherein the heat exchanger is made of a sintered material.
 4. A carriergas heater in accordance with claim 1, wherein the heat exchanger ismade of an open-pore metallic material or ceramic material.
 5. A carriergas heater in accordance with claim 1, wherein the heat exchanger has arecess, in which the heating element is arranged.
 6. A carrier gasheater in accordance with claim 1, further comprising: a housing, whichencloses the gas duct in at least some areas; and a layer, reflectingheat radiation, arranged between the housing and the heat exchanger. 7.A carrier gas heater in accordance with claim 6, wherein the layerreflecting heat radiation is configured as an insulating film.
 8. Acarrier gas heater in accordance with claim 1, further comprising atleast one temperature sensor arranged in the gas duct.
 9. A carrier gasheater in accordance with claim 8, wherein the at least one temperaturesensor is arranged in the area of the heat exchanger.
 10. A carrier gasheater in accordance with claim 1, further comprising temperaturesensors spaced apart from one another in operative connection with thegas duct, wherein each of the temperature sensors sends measuredtemperature values to the control and analysis unit, wherein a controlsignal for operation of the heater is generated in the control andanalysis unit based on a temperature difference between the temperaturevalues detected by the temperature sensors.
 11. A carrier gas heater inaccordance with claim 1, wherein data in relation to at least onehydraulic property of the heat exchanger, which is arranged between thefirst section and the second section of the gas duct, are stored in thecontrol and analysis unit and/or in a memory communicating with thecontrol and analysis unit.
 12. A device for heating a carrier gasstream, which is fed to a patient during anesthesia at least at times,the device comprising a gas heater, the heater comprising: a gas ductwith a gas inlet and with a gas outlet, which are connected by the gasduct; a heater arranged in the gas duct at least partly between the gasinlet and the gas outlet in a flow direction of the carrier gas stream,the heater comprising a heat exchanger with a heat exchanger surfacewhich the carrier gas stream flows over at least partly in an operatingstate, so that the heat exchanger at least at times releases heat to thecarrier gas stream, wherein the gas duct comprises at least one firstsection arranged in the flow direction in front of the heat exchangerand a second section arranged in the flow direction behind the heatexchanger, wherein the heater further comprises a heating element andthe heat exchanger is thermally coupled to the heating element, which issupplied with energy from outside of the gas heater; a first sensorprovided for detecting a pressure value in the first section or directlyadjacent hereto; a second sensor provided for detecting a pressure valuein the second section or directly adjacent hereto; and a control andanalysis unit wherein the detected pressure values are sent to thecontrol and analysis unit and the control and analysis unit isconfigured to determine a mass flow and/or volume flow of the carriergas stream in the gas duct based on a pressure difference of thedetected pressure values, wherein the gas heater is arranged in the flowdirection of the carrier gas stream in front of or behind an anestheticdispenser, which adds at least one anesthetic to the carrier gas stream.13. A process for heating a carrier gas stream, the process comprisingthe steps of: feeding a carrier gas stream to a gas duct via a gas inletand releasing the carrier gas stream from the gas duct via a gas outlet;heating the carrier gas stream between the gas inlet and the gas outletat least at times by a heater, which has a heat exchanger, over a heatexchanger surface of which the carrier gas stream flows at least partlyin an operating state, wherein the heater further comprises a heatingelement and the heat exchanger is thermally coupled to the heatingelement, which is supplied with energy from outside of the heater;detecting a pressure value in the gas duct in a first section arrangedin a flow direction in front of the heat exchanger as well as in asecond section arranged behind the heat exchanger; sending the detectedpressure values to a control and analysis unit; and determining a massflow and/or volume flow of the carrier gas in the gas duct in thecontrol and analysis unit based on a pressure difference of the twopressure values.
 14. A process in accordance with claim 13, wherein atleast one temperature is measured in the gas duct and/or in a componentlocated in the gas duct or adjoining the gas duct.
 15. A process inaccordance with claim 14, wherein a control signal, on which theoperation of the heater is based, is generated based on the measuredtemperature.
 16. A carrier gas heater for heating a carrier gas stream,the gas heater comprising: a gas duct with a gas inlet and with a gasoutlet, which are connected by the gas duct; a heater arranged in thegas duct at least partly between the gas inlet and the gas outlet in aflow direction of the carrier gas stream, the heater comprising a heatexchanger with a heat exchanger surface which the carrier gas streamflows over at least partly in an operating state, so that the heatexchanger at least at times releases heat to the carrier gas stream,wherein the gas duct comprises at least one first section arranged inthe flow direction in front of the heat exchanger and a second sectionarranged in the flow direction behind the heat exchanger, wherein theheat exchanger has a recess, in which a heating element is arranged; afirst sensor provided for detecting a pressure value in the firstsection or directly adjacent hereto; a second sensor provided fordetecting a pressure value in the second section or directly adjacenthereto; and a control and analysis unit wherein the detected pressurevalues are sent to the control and analysis unit and the control andanalysis unit is configured to determine a mass flow and/or volume flowof the carrier gas stream in the gas duct based on a pressure differenceof the detected pressure values.
 17. A carrier gas heater for heating acarrier gas stream, the gas heater comprising: a gas duct with a gasinlet and with a gas outlet, which are connected by the gas duct; aheater arranged in the gas duct at least partly between the gas inletand the gas outlet in a flow direction of the carrier gas stream, theheater comprising a heat exchanger with a heat exchanger surface whichthe carrier gas stream flows over at least partly in an operating state,so that the heat exchanger at least at times releases heat to thecarrier gas stream, wherein the gas duct comprises at least one firstsection arranged in the flow direction in front of the heat exchangerand a second section arranged in the flow direction behind the heatexchanger; a first sensor provided for detecting a pressure value in thefirst section or directly adjacent hereto; a second sensor provided fordetecting a pressure value in the second section or directly adjacenthereto; a control and analysis unit wherein the detected pressure valuesare sent to the control and analysis unit and the control and analysisunit is configured to determine a mass flow and/or volume flow of thecarrier gas stream in the gas duct based on a pressure difference of thedetected pressure values; and temperature sensors spaced apart from oneanother in operative connection with the gas duct, wherein each of thetemperature sensors sends measured temperature values to the control andanalysis unit, wherein a control signal for operation of the heater isgenerated in the control and analysis unit based on a temperaturedifference between the temperature values detected by the temperaturesensors.